1. Field of the Invention
The present invention generally relates to a manifold assembly for an atomic layer deposition (ALD) reactor.
2. Description of the Related Art
Atomic layer deposition (ALD) is a well known process in the semiconductor industry for forming thin films of materials on substrates such as silicon wafers. ALD is a type of vapor deposition wherein a film is built up through deposition of multiple ultra-thin layers with the thickness of the film being determined by the number of layers deposited. In an ALD process, gaseous molecules of one or more compounds (precursors) of the material to be deposited are supplied to the substrate or wafer to form a thin film of that material on the wafer. In one pulse, typically less than 1 monolayer of a first precursor material is adsorbed largely intact in a self-limiting process on the wafer. The adsorbed precursor material may be decomposed or otherwise reacted in a subsequent reactant pulse or pulses to form a single molecular layer of the desired material. For example, the adsorbed precursor material may react with the reactant of a subsequent reactant pulse to form a single molecular layer of an element or a compound. Examples include reactant pulses that merely strip ligands from the adsorbed species, reactants that replace ligands with other species to form compounds, and sequences with three or more reactant and/or precursor pulses per cycle. Thicker films are produced through repeated growth cycles until the target thickness is achieved.
In an ALD process, one or more substrates with at least one surface to be coated are introduced into the reactor or deposition chamber. The wafer is typically heated to a desired temperature above the condensation temperature but below the thermal decomposition temperature of the selected vapor phase reactants. One reactant is capable of reacting with the adsorbed species of a prior reactant to form a desired product on the substrate surface. The product can be in the form of a film, liner, or layer.
During an ALD process, the reactant pulses, all of which are typically in vapor or gaseous form, are pulsed sequentially into the reactor with removal steps between reactant pulses. For example, inert gas pulses are provided between the pulses of reactants. The inert gas purges the chamber of one reactant pulse before the next reactant pulse to avoid gas phase mixing or CVD type reactions. A characteristic feature of ALD is that each reactant (whether a precursor contributing species to the film or merely a reducing agent) is delivered to the substrate until a saturated surface condition is reached. The cycles are repeated to form an atomic layer of the desired thickness. To obtain a self-limiting growth, sufficient amount of each precursor is provided to saturate the substrate. As the growth rate is self-limiting, the rate of growth is proportional to the repetition rate of the reaction sequences, rather than to the flux of reactant and/or temperature as in CVD.